A timing belt is the toothed belt that drives a camshaft in step with the crankshaft. It’s also called a cambelt, a cam belt, a toothed belt or a synchronous belt.
Below: what a timing belt does, the automotive and industrial split, materials, tooth profiles, belt versus chain, and how belts fail. Pitch codes, belts that run in oil, the replacement interval, tension and noise each have their own page.
Key Takeaways
- A timing belt, or cambelt, drives the camshaft in step with the crankshaft so the valves open and close at the correct times relative to piston position.
- Camshafts turn at half the speed of the crankshaft. Evenly spaced teeth give a positive drive: correctly tensioned, the belt does not slip and needs no lubrication.
- The same toothed belt is a camshaft drive on car and motorcycle engines and an indexing belt on machines such as sewing machines and photocopiers.
- The body is typically rubber, sometimes polyurethane or neoprene, with cord tension members and a fabric cover on the teeth.
- A belt wears and is replaced at intervals. A worn chain usually rattles, while a rubber belt gives no indication of impending failure.
Table of Contents
- What a timing belt does
- Automotive and industrial timing belts
- What a timing belt is made of
- Timing belt tooth profiles
- Timing belt or timing chain
- How timing belts fail
- Replacement and maintenance: where to go next
- FAQ
- About Longyi Rubber Products Factory
What a timing belt does
What does a timing belt do? Wikipedia on the camshaft timing belt describes the belt, also called a cambelt, as a toothed belt that drives the camshaft and synchronizes its rotation with the crankshaft. The valves open and close at the correct times relative to piston position.
The pistons keep moving while the valves open and close, so the belt is the link that keeps the camshaft turning in step with the crankshaft. Lose the link, and those events no longer match piston position.
The shafts do not turn at the same speed. Samarins on timing belts states that camshafts turn at half the speed of the crankshaft: two crankshaft revolutions for each camshaft revolution. In some engines the belt also drives the water pump, a balance shaft, an intermediate shaft, the injection pump or the oil pump.
Teeth make the ratio hold. SDP/SI technical section on timing belts describes these belts as flat belts with evenly spaced teeth on the inside circumference. There is no slippage or creep, as there is with a plain flat belt. A synchronous belt does not require lubrication.
Automotive and industrial timing belts
The teeth can look alike, but the job differs.
On an engine, this belt is the camshaft drive. Wikipedia on toothed belts places toothed belts in sewing machines and photocopiers, among many other devices, and as the camshaft drive of car and motorcycle engines. The automotive belt keeps the valves and the pistons in step.
For a car, the replacement interval is set by the vehicle maker; the last section below covers it.
An industrial synchronous belt times a machine instead of a valve. Correctly tensioned, the teeth do not slip, and the belt transfers motion for indexing or timing. Wikipedia on toothed belts says these belts are used instead of chains or gears, with less noise and with no lubrication bath. Indexing means the driven shaft holds a set position relative to the shaft that drives it.
Timing belt types start with this split. An automotive timing belt serves the camshaft drive. An industrial timing belt serves indexing or shaft timing.
They are listed separately: automotive timing belts and industrial timing belts. Send the belt code, a drawing or the size. For an industrial drive, the timing belt tensioning guide covers tension.
What a timing belt is made of
A rubber timing belt is the usual build. Wikipedia on the camshaft timing belt says a timing belt is typically made from rubber, although some belts are made from polyurethane or neoprene. Corded fibers act as the tension members. The toothed surface is covered with fabric.
Wikipedia on toothed belts describes toothed belts as a flexible polymer over a fabric reinforcement. Materials moved from natural rubber to synthetic rubber and polyurethane, with steel, nylon, aramid or carbon fiber reinforcement.
Rubber, polyurethane and neoprene are the body materials. Steel, nylon, aramid and carbon fiber are reinforcements, and the fabric stays on the tooth. If the printing on a belt is gone, measure the outside length and count the teeth.
Body material and cord material are separate choices: polyurethane tells you nothing about the cord, and a steel cord tells you nothing about the body.
Timing belt tooth profiles
Tooth shape is the next split in timing belt types. SDP/SI technical section on timing belts says the tooth profile of the most commonly known synchronous belts is trapezoidal. It was superseded by a curvilinear profile with a deeper tooth. With that later profile, tooth jumping is less probable, the contact area is larger, and the shear strength is greater.
A trapezoidal tooth has straight flanks. A curvilinear tooth has a curved flank. Tooth jumping means the tooth leaves the pulley groove and the shafts slip out of time.
A pulley takes one tooth profile, so order the profile and pitch your pulley was cut for.
Pitch codes are on the HTD timing belt page.
Timing belt or timing chain
Wikipedia on the camshaft timing belt calls the belt a semidurable component. In some cases it lasts for the life of the engine, and in others it must be replaced once to several times, depending on use and how long the vehicle is in service.
Other engines use a chain or gears instead.
- A belt has lower cost, less friction loss and less noise than a chain, and it traditionally needs no lubrication (Wikipedia on the camshaft timing belt). It also wears, so it must be replaced at intervals.
- Chains have become more widespread in car engines since the 1990s to eliminate regular interval replacement. A worn chain usually rattles, while a rubber belt gives no indication of impending failure (Wikipedia on the camshaft timing belt).
Check the owner’s manual for the interval, and for which drive that engine uses.
How timing belts fail
Timing belt failure is usually a tooth problem or a bond problem. Wikipedia on the camshaft timing belt names stripped teeth, and delamination or unraveling of the fiber cores. Breakage is uncommon. Dirt mixed with oil or grease can wear the belt and cause premature failure.
Wikipedia on toothed belts describes two endings. Gradual wear of the tooth shape can end in slippage, so the timing between the shafts shifts. The other ending is delamination between the belt and its fabric reinforcement. Oil at the edges, and overbending, twisting or knotting during install or storage, are common causes.
Stripped teeth have come off the belt, so the pulley is no longer driven in step; a worn tooth can slip while the belt is still in one piece. Do not knot, twist or overbend a belt.
Many modern cars use interference engines. Wikipedia on the camshaft timing belt says loss of synchronization then makes the valves collide with the pistons, which can cause catastrophic damage. A failing tensioner, idler bearing or water pump can also derail or break the belt.
Noise and tension have their own pages: timing belt squeal causes and fixes for the sound, and the timing belt tensioning guide for tension.
Replacement and maintenance: where to go next
AAA on when to replace a timing belt gives the range most auto manufacturers recommend: somewhere between 60,000 and 100,000 miles, varying by vehicle, and it says to check the owner’s manual.
Wikipedia on the camshaft timing belt gives no mile figure. In some cases the belt lasts for the life of the engine, and in others it is replaced once to several times, depending on use and how long the vehicle is in service. The maker’s service information for the specific engine decides.
When the belt is changed, the parts on that drive are part of the job. Brake & Front End on timing belt aging reports one belt supplier’s advice: when changing belts, replace all the relevant belt drive components at the same time.
The car interval is on the timing belt replacement interval page. A belt that runs in oil is a wet timing belt, and that service question is separate.
FAQ
What does a timing belt do?
A timing belt drives the camshaft in step with the crankshaft so the valves open and close at the correct times relative to piston position (Wikipedia on the camshaft timing belt). The camshaft turns at half crankshaft speed, and on some engines that belt also drives a water pump or another shaft.
Is a timing belt the same as a cam belt?
Yes. A cam belt, or cambelt, is the same belt (Wikipedia on the camshaft timing belt). Toothed belt and synchronous belt are wider names, and they also cover sewing machines, photocopiers and many other devices.
Timing belt or timing chain: what is the difference?
A belt wears and is replaced at intervals. Chains have become more widespread in car engines since the 1990s to eliminate that regular replacement, and a worn chain usually rattles while a rubber belt gives no warning (Wikipedia on the camshaft timing belt). Belts traditionally need no lubrication, with lower cost, less friction loss and less noise.
What happens if a timing belt breaks?
Breakage is uncommon. Stripped teeth and delamination or unraveling of the fiber cores are the usual modes, and on an interference engine the valves can collide with the pistons and cause catastrophic damage (Wikipedia on the camshaft timing belt).
How do I know whether my engine has a timing belt or a chain?
Not all cars have a timing belt, and many newer cars use a chain. Check the owner’s manual, or ask a dealer service department or a mechanic (Samarins on timing belts).
What should I send to get a replacement timing belt?
Send the belt code, a drawing or the size, and say whether the belt is for a car engine or an industrial drive. The automotive and industrial ranges are listed separately.
Sources
- Wikipedia on the camshaft timing belt
- Samarins on timing belts
- SDP/SI technical section on timing belts
- Wikipedia on toothed belts
- AAA on when to replace a timing belt
- Brake & Front End on timing belt aging
Source names appear here only as references. LYBELT is not affiliated with them.
About Longyi Rubber Products Factory
LYBELT is the brand of Longyao County Longyi Rubber Products Factory (General Partnership), based in Longyao County, Xingtai, Hebei, China, and making rubber belts since 1999. The factory holds IATF 16949 and ISO 9001 certification and works from 130+ rubber compounds.
The range covers automotive, industrial, agricultural, ATV/UTV and motorcycle belts. For OEM and ODM orders, belts are made to the customer’s part number, drawing or size, with private label and packaging. Email: luxin@lybelt.com.